1. Field of the Invention
The invention relates to a backlight module, more particularly to a backlight module capable of simultaneously providing light for image display and keyboard illumination, and a planar display device and a portable electronic device incorporating the same.
2. Description of the Related Art
Referring to FIG. 1, in Taiwanese Patent Application No. 494295, there is disclosed a notebook computer 1 including a cover body 10 that is provided with a display screen 11 and an LED lamp 12 at an upper end of the display screen 11 for illuminating a keyboard 14 of a main body 13 of the notebook computer 1 in a projecting manner. Referring to FIG. 2, according to the same patent, there is disclosed a light emitting keyboard 2 that includes a plurality of keys 21 and a light source module 22. Each of the keys 21 has a key cap 23 with a translucent region 24. The light source module 22 includes a light guide plate 25 disposed below the keys 21, and at least one light emitting component 26 mounted at a corner of the light guide plate 25. The light emitting component 26 emits light toward the light guide plate 25 for the light to be guided to travel along a light guide route (L) to pass through the translucent regions 24 of the keys 21. For keyboard illumination in the above manners, the light source (i.e., the LED lamp 12 of FIG. 1 and the light source module 22 of FIG. 2) is additionally and specifically provided for this purpose. In addition, for the light emitting keyboard 2, in addition to providing the light source module 22, the key caps 23 have to be specially manufactured to provide the translucent regions 24, increasing difficulty and cost of fabrication.
Referring to FIG. 3, a conventional edge type backlight module 3 for a liquid crystal display device includes an LED light source 31, and a reflecting plate 32, a light guide plate 33, a light diffusion plate 34, a light enhancing plate 35 and a light mask plate 36 arranged side by side in sequence from the LED light source 31. The LED light source 31 emits light to the light guide plate 33 so as to be guided thereby to travel in the same direction, such as a non-perpendicular direction away from an upper surface of the light guide plate 33. The light diffusion plate 34 diffuses the light from the light guide plate 33 uniformly to form a surface light. The light enhancing plate 35 focuses the light from the light diffusion plate 34 so as to increase forward luminance. The light mask plate 36 prevents the light from the light enhancing plate 35 from escaping from the peripheries of the conventional edge type backlight module so as to decrease optical loss and ensure that the light be projected onto a liquid crystal panel 37 arranged on the side of the light mask plate 36 opposite to the light enhancing plate 35. The current technology of the light guide plate 33 is unable to ensure that 100% of the light emitting from the LED light source 31 be guided to travel in that same direction. Therefore, the light reflecting plate 31 is provided to reflect light escaping from the light guide plate 33 in the wrong direction back toward the light guide plate 33.